A Localytics study issued today helps understand why Verizon Wireless recently sided with Samsung in the ongoing Apple vs. Samsung legal saga. Per Localytics’ data, 4G is one of Android’s key differentiators: More than one in three Android phones in the United States take advantage of fourth-generation cellular networks. In the third quarter of this year, some 36.6 percent of Android handsets in the United States were 4G-ready, a notable increase over the 22.6 percent in the first quarter of 2011.

This number is increasing rapidly – since the beginning of the year, the percentage of Android devices that are 4G-capable has grown by over 50 percent, culminating at a full third of the Android ecosystem. It will be interesting to see whether the iPhone 5 supports any type of 4G network. The drawbacks – bulkier antenna and a much shorter battery life – may outweigh the benefits in speed. Regardless, with the growth in 4G-capable handsets Android has seen, it appears that smartphone users are buying into the value of speed. We’ll see how this continues.

The nation’s most popular 4G handsets in the third quarter were the HTC Thunderbolt (Verizon), the HTC Evo 4G (Sprint), the Samsung Epic 4G (Sprint), the Samsung Droid Charge (Verizon), the myTouch 4G (T-Mobile USA) and the Motorola Atrix (AT&T). A few caveats and the full list of most popular 4G devices in the country right below the fold…

The study defines 4G as HSPA+ (T-Mobile USA, AT&T), LTE (Verizon Wireless) or WiMAX (Sprint Nextel) radio technologies. However, there is a disconnect between what the public perceives as a fourth-generation network (the one using Long-Term Evolution radio technology) and what the carriers are advertising as a 4G network. This is especially true in the case of T-Mobile USA which lacks true 4G LTE network, but that’s not stopping them from advertising their 42Mbps-capable 3G HSPA+ network as 4G-capable. AT&T too hinted it would love to promote the next iPhone as being 4G capable. The Next Generation Wireless Disclosure Act is lawmakers’ answer to such a dubious practice. The bill, proposed in the US House of Representatives in June, seeks to force carriers to detail their 4G coverage and guaranteed minimum data speeds when you sign up for a 4G device or service.